362 MY LIFE 



these causes must be enormous in order to keep down the 

 numbers of each species, since they evidently do not increase 

 regularly from year to year, as otherwise the world would long 

 ago have been densely crowded with those that breed most 

 quickly. Vaguely thinking over the enormous and constant 

 destruction which this implied, it occurred to me to ask the 

 question, Why do some die and some live? And the answer 

 was clearly, that on the whole the best fitted live. From the 

 effects of disease the most healthy escaped ; from enemies, 

 the strongest, the swiftest, or the most cunning; from famine, 

 the best hunters or those with the best digestion ; and so on. 

 Then it suddenly flashed upon me that this self-acting process 

 would necessarily improve the race, because in every genera- 

 tion the inferior would inevitably be killed off and the 

 superior would remain — that is, the fittest would survive. 

 Then at once I seemed to see the whole effect of this, that 

 when changes of land and sea, or of climate, or of food- 

 supply, or of enemies occurred — and we know that such 

 changes have always been taking place — and considering the 

 amount of individual variation that my experience as a col- 

 lector had shown me to exist, then it followed that all the 

 changes necessary for the adaptation of the species to the 

 changing conditions would be brought about; and as great 

 changes in the environment are always slow, there would be 

 ample time for the change to be effected by the survival of 

 the best fitted in every generation. In this way every part 

 of an animal's organization could be modified exactly as 

 required, and in the very process of this modification the 

 unmodified would die out, and thus the definite characters 

 and the clear isolation of each new species would be explained. 

 The more I thought over it the more I became convinced that 

 I had at length found the long-sought-for law of nature that 

 solved the problem of the origin of species. For the next 

 hour I thought over the deficiencies in the theories of Lamarck 

 and of the author of the " Vestiges," and I saw that my new 

 theory supplemented these views and obviated every important 

 difficulty. I waited anxiously for the termination of my fit 

 so that I might at once make notes for a paper on the subject. 



